1. Field of the Invention
This invention relates to a control signal generator for a camera arranged to generate a control signal indicative of the opened or closed position of the blades of a shutter which also function as a stop.
2. Description of the Prior Art
In a camera of the kind having a shUtter which also functions as a stop, a photo interrupter is formed by light emitting and receiving elements which are opposed to signal generating openings provided in a shutter blade. The position of shutter blades is detected by means of the photo interrupter. Japanese Laid-Open Patent Application No. SHO 58-46329 discloses a camera of this kind. In this camera, the photo interrupter first produces a signal when the shutter blades begin to move. This signal is used for closing a count swiTch for exposure control or for an automatic flashing operation. Following the first signal, the positions of the shutter blades are detected by the second and subsequent openings to produce signals accordingly. However, according to the arrangement of the photo interrupter disclosed in this patent application, the first signal and the second and subsequent signals are obtained from the same shutter blade. Therefore, a time difference between the first and second signals is naturally restricted. FIG. 1 of the accompanying drawings shows the details of the arrangement of the prior art. In FIG. 1, only the essential parts forming a shutter are shown as viewed from behind the optical path of the camera with the shutter in a closed state. A first shutter blade 1 which turns on a shaft 3 and a second shutter blade 5 which turns on another shaft 7 partly overlap each other to completely close a full open aperture R which is indicated by a broken line. These shutter blades 1 and 5 are provided with V-shaped stop blade portions as they are performing combined functions as shutter blades and stop blades. When the blades 1, 5 turn in the directions of arrows X and X' to uncover the aperture, their V-shaped opening portions jointly define a stop aperture. The shutter blade 1 has signal generating openings 1a1, 1a2, 1a3,--formed in its peripheral part along the turning locus thereof. Meanwhile, a couple of light emitting and receiving elements 10 are disposed to confront the turning locus X of the blade 1 and thus serve as a photo interrupter. The output of the photo interrupter first changes when an edge part 1b of the shutter blade 1 reaches the couple of elements 10. This change becomes a first signal. A second signal is obtained when the openings 1a1 is read. Then, each of the second signals and signals subsequent thereto corresponds to an aperture position. With the photo interrupter arranged in this manner, however, the first signal is produced after the lapse of a length of time from the commencement of the movement of the shutter blade 1. The first signal would be obtainable soon after the commencement of the movement of the shutter blade 1 if the couple of elements 10 are disposed close to the edge part 1b of the shutter blade 1. However, if the control arrangement of the camera requires a long time interval between the first signal and the aperture position signal which is one of the second and subsequent signals, the distance between the edge part 1b and the opening 1a1 of the shutter blade 1 must be long. Then, this causes an increase in the size of the shutter blade 1 and thus results in an increased camera size.
Furthermore, an automatic flash photography device is also disclosed in the same Japanese patent application cited in the foregoing. According to the exposure control arrangement disclosed in that application, after the shutter begins to open, a shutter closing signal is produced either when the exposure gradually integrated reaches a value set for an apposite degreee of exposure after a time lapse or when a hand vibration preventable limit time (a time limit normally set at about 1/30 sec.) is reached, whichever is shorter. In carrying out a flash photography operation, a signal which causes the flash device to flash is produced concurrently with a shutter closing signal. FIG. 2 shows the variation of the aperture of the shutter blades 1, 5 (or stop blades) which takes place when the hand vibration preventable limit time is shorter than the length of time required for the integrated value corresponding to the set value of the apposite amount of exposure. Referring to FIG. 2, the shutter blades 1, 5 begin to open at a point S. The flash device flashes at a point B which is a time limit point in this instance. However, if flash photography is to be carried out in a dark external light condition, an exposure based on the external light and an exposure based on the flash light overlap each other. Besides, since the hand vibration preventable limit time is relatively long, a blur due to hand vibration tends to occur. If, the limit time is set at a shorter time value, the problem hand vibration may be solved. However, the shutter blades 1, 5 bounce back to a slight extent immediately after they are opened, as indicated by a range D. The limit time, therefore, sometimes lapses during the process of such a bounce. Because of this, the limit time cannot be shortened too much and thus cannot always be set at a desired time value.
This invention is directed to the solution of the above-stated problems of the prior art devices. It is therefore an object of the invention to provide a compact control signal generator for a camera, wherein openings, are provided in one of the shutter blades 1 for enabling a photo interrupter to detect the opening degree of the shutter; and the shutter blade 5 other than the specific blade 1 blocks, when the shutter is in a closed state, an optical path which the light emitting and receiving elements of a photo interrupter are confronting, so that signal generating timing can be set with great latitude.
It is another object of the invention to provide a compact control signal generator for a camera, wherein a flash device flashes when a photo interrupter detects a full open state of stop blades, so that flash photography can be carried out without being affected by hand vibrations even in a dim light.
These and further objects and features of the invention will become apparent from the following detailed description of a preferred embodiment thereof taken in conjunction with the accompanying drawings.